1. Technical Field
The present invention relates generally to ventilation control systems, and more particularly to a multi zone ventilation modeling system that integrates the ventilation control concepts of flow rate and age of air, thereby enabling the methodology to be used for ventilation control and ventilation performance evaluation, and that results in a ventilation control strategy that minimizes the amount of outdoor air required to maintain the age of air in each of the zones in a multi zone system at or below a specified age level.
2. Discussion
It is common practice to utilize ventilation strategies to control concentration of contaminants within buildings. Ventilation, which is a dilution process that involves mixing uncontaminated outdoor air with contaminated, or recycled, indoor air, allows contaminant concentrations to be maintained at or below predetermined acceptable levels. Two important variables in the ventilation process include: 1) the required quantity of uncontaminated air necessary to keep contaminant levels in the building at or below predetermined acceptable levels; and 2) the air mixing effectiveness of the building ventilation system.
ASHRAE Standard 62 provides specific guidelines for minimum acceptable ventilation system parameters. The standard describes the minimum parameters in terms of outdoor air flow rates, and, as a result, the parameters constitute constraints on the ventilation control system. When a parameter within a zone in a multi zone ventilation system reaches its maximum or minimum allowable value, the zone is referred to as a critical zone. Generally, and particularly in variable air volume (VAV) ventilation control systems, a critical zone changes dynamically.
Considerable attention has been focused on methods of meeting the minimum requirements of ASHRAE Standard 62, while using the minimum required amount of unconditioned outdoor air, as use of unconditioned outdoor air results in increased ventilation costs. Methods of meeting the requirements of Standard 62 become more complicated when multi zone systems are modeled. One conventional method of addressing the above problem is generally referred to as the Multiple Spaces Methods (MSMs). However, while Standard 62 requires compensation for poor ventilation effectiveness, which is a measure of the amount of stagnant air in a space, conventional approaches, such as MSMs, often fail to address this parameter.
While conventional MSMs exhibit adequate performance characteristics on many applications, such conventional ventilation strategies do have associated drawbacks. For instance, MSMs do not account for spaces that receive neither primary air from air and air handling units, nor secondary air from a plenum, but that do have an associated ventilation constraint. Such spaces often include bathrooms and hallways. In addition, MSM either do not calculate, or have typically have associated difficulty calculating, flow rates between zones in a multi zone system. Such flow rates, if known, could be used to decrease the ventilation requirements in the multi zone systems resulting from overventilated zones. In addition, MSMs do not account for local exhaust, such as bathroom exhaust. As almost all buildings have such local exhaust systems, it would be desirable to provide a ventilation control strategy that would account for such local exhaust. Finally, and in general, as all MSMs require the use of a certain amount of outdoor air, it is always desirable to provide a ventilation control strategy that minimizes the amount of outdoor air required, while still meeting ASHRAE Standard 62 requirements.